The books don't really specify that *all* civilizations are actively hostile to each other but hints that the best chance for survival is basically being quiet since there are unknown civilizations that yield tremendous power and are in fact actively hostile to any signs of other intelligent life which they can destroy with relative and terrifying ease. It's that sort of status-quo that makes the dark forest theory so scary and why everybody that eventually reaches that conclusion would want to remain hidden and/or silent. Throughout the story we only ever get to see from the point of view of two civilizations so who knows if there wasn't something like a star-trekian federation at some place or time since we do eventually get to know that there were many many civilizations in the end.

It does get really crazy, but I personally found the whole trilogy really awesome. It would be hard to build such a story relying only on our current understanding of physics and technology and even some of the crazier parts are still kind of based out of real theories and hypothetical developments or discoveries.

I still highly recommend this trilogy to any sci-fi/first contact fan.